Aircraft: B747
Phase of flight: Climb
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy

Passing FL280 on departure we received a 'ENG 4 Fuel Filter' EICAS message. We ran the appropriate QRH checklist which ends with the statement 'Only one ENG FUEL FILTER message has shown during the flight: Note: Erratic engine operation and flameout may occur on the affected engine due to fuel contamination.' We elected to proceed. Later shortly the 'ENG 3 Fuel Filter' EICAS message illuminated momentarily. Once again we ran the QRH checklist and in this instance the following statement applied: 'ENG FUEL FILTER messages for more than one engine shown or have shown at any time during the flight (either separately or at the same time): Plan to land at the nearest suitable airport.' Our SATCOM was inoperable in the voice mode so we used the HF radio to set up a phone patch with Dispatch. In a three-way phone conversation with Dispatch and Maintenance Control we discussed a divert to ZZZZ. ZZZZ; at this point was roughly 860 miles away while ZZZ was 1650 miles. Also discussed was whether ZZZZ was able to handle 416 passengers with families as well as what maintenance assets were available and therefore qualified as 'suitable'. During this conversation; both the ENG 4 and ENG 3 Fuel Filter EICAS messages reilluminated and that sealed the deal. We headed for ZZZZ and would take care of the other considerations later. We received a diversion flight plan over the ACARS from Dispatch and coordinated with ARTCC for the change. The flight to ZZZZ was uneventful other than having the ENG 3 Fuel Filter ECAS remaining on for the rest of the flight. We landed and after shutdown; our on-board mechanic called Maintenance control to coordinate the repairs. We were told that we should be fixed and on our way in an hour or two. This seemed optimistic; and we considered options to care for the passengers should the process become protracted. As time passed and it became apparent that this would take much longer; we coordinated for transportation and deplaned our passengers to be taken to a holding area where they would be much more comfortable. Meanwhile; our mechanic had secured the engines; opened both cowlings and removed the fuel filters. No obvious contamination was found in the filters or the fuel however he did discover that both filters were old and had been in place for some time. These filters are to be changed as part of an 'A' check and in his opinion these particular filters had not been for a least one cycle of checks. Two new filters from our on-board kit were installed and after the engines were closed back up and an engine run leak check was performed the repairs were complete. By this time; the fueler had left the aircraft. We were informed that he was now working the afternoon's airline flights and it would be another two hours before he could get back to us. Later; once we received word that our fuel was on the way we called for the passengers to be recalled to the aircraft. After a ground time of 4+18 we departed. B747 Captain reported receiving two 'ENGINE FUEL FILTER' EICAS messages in flight and diverting.